The present invention relates to a device for separating reserve turns of thread for devices that feed weft to weaving looms, particularly shuttle-less gripper, projectile and fluid-jet looms.
As is known, weft feeders for looms of the specified type, or more generally for textile machines, are devices provided with a fixed drum; multiple turns of thread to be fed to the loom are wound at the base of said drum by means of a suitable flywheel which has a windmilling arm rigidly coupled to a drive shaft of the device. These turns constitute a reserve of thread which must be proportionate to the beat rate of the loom to be fed and are unwound from the opposite end--briefly termed dome--of the drum; the turns that are gradually removed are replaced by an advancement system which moves said turns from the base to the dome of the drum, keeping them mutually spaced by a given pitch that determines the number of turns wound, and thus the amount of the thread reserve.
The known and now universally adopted advancement system uses a swift which is formed by a set of rotationally rigidly coupled axial rods which partially and variably protrude from respective axial slots, provided on the drum by virtue of a compound motion which is applied to the swift by the drive shaft of the feeder by means of a tilted bush which is fitted on an eccentric portion of said drive shaft. The motion applied to the swift by said bush and by the eccentric portion of the shaft is substantially the result of a sinusoidal undulatory component and of an oscillatory component on the axial plane and makes the turns of thread advance axially along the drum; the direction of said advancement depends on the direction of the rotation of the drive shaft. Since the turns must always advance from the base towards the dome of the drum, if the direction of the rotation of the drive shaft is changed--for example to adapt the device to threads with left-handed or right-handed twisting--the bush must be correspondingly replaced with another one which is mirror-symmetrical, so as to reverse the inclination of the swift with respect to the drum.
This operation entails disassembling the swift from the drive shaft, extracting the bush of one kind, mounting the bush of the other kind, and reassembling the swift.
In an attempt to obviate this troublesome series of operations that require long downtimes of the feeder, special bushes have been provided which are more simply rotated about their axis and are fixed, by means of transverse locking screws, in two mirror-symmetrical active positions which are angularly spaced by 180.degree.. A bush of this type is described in U.S. Pat. No. 4,632,154.
This known type of bush, however, only partially solves the problem of rapidly adapting the feeder to the various kinds of thread and does not allow to vary the inclination of the swift within intermediate values and thus vary the pitch of the turns wound on the drum.
According to another known solution, described in European patent no. 0,326,960, the eccentric portion of the drive shaft is hollow and a ring with a spherical surface is keyed to it; bush portions rigidly coupled by axial traction elements abut on either side of said ring and are rotationally coupled to it. Each bush portion has an axial hole which is larger in diameter than the eccentric part of the shaft, so that the bush, under the actuation of kinematic movement means which are accommodated within the cavity of the shaft and can be accessed from outside the drum, can rotate on an axial plane with respect to the ring so as to tilt on one side or the other with respect to the axis of said shaft.
Other solutions of this type, which include a tilting bush having a larger internal diameter than the drive shaft, are described in U.S. Pat. No. 4,747,549 and in international patent application WO 90/00149.
Another known solution aimed at achieving the automatic adaptation of the tilt of the bush to the direction of rotation of the drive shaft is described in German patent application no. DE 4105174.
This solution uses a tilted bush which is rotatably mounted on a sleeve that is fitted on the drive shaft and has a slot which is shaped like a 180.degree. circular arc; an actuation pawl cooperates with the slot and engages the one end shoulder of the slot or the other, performing a 180.degree. idle stroke every time the direction of the rotation of the shaft reverses.
Although the above described known devices considerably simplify or automate the operations for adapting the feeder to the different types of thread, they all have the drawback of considerable structural complexity, with the possibility of wear of the kinematic systems that control the tilt of the bush and of the consequent formation of plays which in addition to negatively affecting the correct operation of the device facilitate breakages, reducing the operating reliability of the weft feeder. Furthermore, the above mentioned known solutions all entail the adoption of drive shafts having eccentric portions that cooperate with the swift control bush, and this considerably complicates the construction of said shaft, with evident economical and functional drawbacks which are even worse in the solutions in which the shaft also has an axial cavity that accommodates the kinematic control systems that vary the tilt of the bush of the swift.